Search

Vapochromic crystals of Ni(II)-quinonoid complexes were theoretically investigated using density functional theory (DFT) calculations. Kato et al. previously reported that the purple crystals of a four-coordinate Ni(II)-quinonoid complex (

The emission spectrum of the platinum(II) bipyridine complex [Pt(CN)2(bpy)] (bpy = 2,2′-bipyridine) interestingly exhibits blue shift and peak broadening in crystal as temperature increases from 15...

A dissociative force field for all-atomistic molecular dynamics calculations has been developed to investigate impact fracture of polymers accompanying dissociation of chemical bonds of polymer main chain. Energy of dimer molecules was evaluated as a function of both bond-length b and bond-angle θ by CASPT2 calculations, whose quality is enough to describe dissociation of chemical bonds. Because we found that the bond dissociation energy D decreases with increasing bond-angle, we employed the Morse-type function VBond (b, θ) = {D - VAngle (θ)}[1 - exp{-α(b - b0 ) - β(b - b0 )2 }] where a quartic function VAngle (θ) = k1 (θ - θ0 ) + k2 (θ - θ0 )2 + k3 (θ - θ0 )3 + k4 (θ - θ0 )4 . This function reproduced well the CASPT2 potential energy surface in a wide range of b and θ. The parameters have been obtained for four popular glassy polymers, polyethylene, poly(methyl methacrylate), poly(styrene), and polycarbonate. © 2019 Wiley Periodicals, Inc.

Trinuclear Cr(ii) complex [Cr3(dpa)4Cl2] 1 (Hdpa = dipyridylamine) has two Cr-Cr double bonds linked with each other. DMRG-CASPT2 calculations reproduced its symmetrical structure. The Cr-Cr effective bond order (EBO) was evaluated to be only 0.59 based on the density matrix based on localized orbitals from DMRG-CASSCF orbitals. The CASCI calculations showed a significantly large α-spin population on the terminal Cr atoms as expected but a significantly large β-spin population on the central Cr atom against expectations. The very small EBO and the presence of a large β-spin population are not consistent with the simple understanding that 1 has two Cr-Cr double bonds and a quintet ground state, which requests correct understanding of 1 from the viewpoint of chemical bond theory. Comparison of 1 with the allene molecule and allyl radical disclosed that the linked Cr-Cr bonds of 1 resembled the C-C bond of the allyl radical but completely differed from the linked C-C double bonds of allene despite the similar molecular structure. Its N3 analogue [Cr3(dpa)4(N3)2] 2 has non-symmetrical structure with shorter Cr1-Cr2 and longer Cr2-Cr3 bonds unlike 1, indicating that 2 is a valence tautomer of 1. DMRG-CASPT2 could reproduce its non-symmetrical structure but DFT/B3PW91 could not. In 2, the EBO is 0.95 for the shorter Cr1-Cr2 bond and 0.47 for the longer Cr2-Cr3 one. The terminal Cr3 has a very large α spin population, and the other terminal Cr1 has a somewhat large α spin population, but the central Cr2 has a considerably large β spin population. These results indicate that the Cr1-Cr2 bond conjugates with the Cr2-Cr3 bond, which is inconsistent with the simple understanding that 2 has a quadruple bond between Cr1 and Cr2 and no bond between Cr2 and Cr3. The symmetrical structure has a stronger Cr-X coordinate bond (X = Cl or N3) but less stable Cr3 core than does the non-symmetrical one. The relative stabilities of the symmetrical and the non-symmetrical structures are determined by the balance between stabilization energies from the Cr3 core and the Cr-X coordinate bond. All these findings show that electronic structures and Cr-Cr bonds of 1 and 2 are interesting from the viewpoint of molecular science.

Experimentally observed NO dimerization on Cu and Ag surfaces is surprising because binding energy of NO dimer is very small in gas phase. MRMP2, MP2 to MP4, CCSD(T), and DFT studies of NO dimerization on Ag2 and Cu2 clusters disclosed that the CCSD(T) method could be applied to this reaction on Ag2 and Cu2 unlike NO dimerization in gas phase which exhibits significantly large nondynamical electron correlation effect. Charge-transfer (CT) from Ag2 and Cu2 to NO moieties plays important role in NN bond formation between two NO molecules. This CT considerably decreases nondynamical correlation effect. Also, the DFT method could be applied to this NO dimerization, if appropriate DFT functional is used; all pure functionals examined here and most of the hybrid functionals underestimated the activation barrier (Ea ), while only ωB97X provided Ea similar to CCSD(T)-calculated value. NO dimerization on similar Cu2 and Cu5 needs moderately larger Ea than those on Ag2 and Ag5 , because frontier orbital participating in the CT exists at lower energy in Cu2 and Cu5 than in Ag2 and Ag5 . The Ea decreases in the order Ag2 >> Ag38 > Ag7 ∼ Ag5 and the reaction energy (ΔE) is positive (endothermic) in Ag2 but significantly negative in Ag38 , Ag7 , and Ag5 , indicating that various Ag clusters could be effective for NO dimerization except for Ag2 . The decreasing order of Ea and increasing order of exothermicity are attributed to increasing order of the frontier orbital energy of Ag2 < Ag38 < Ag7 ∼ Ag5 . © 2018 Wiley Periodicals, Inc.

Reactions of silanone(silyl)tungsten and -molybdenum complexes Cp*(OC)2M{O═SiMes2(DMAP)}(SiMe3) (M = W (1a), Mo (1b), Cp* = η5-C5Me5, Mes = 2,4,6-Me3C6H2, DMAP = 4-(Me2N)C5H4N) with MesCNO, (Me2SiO)3, MeOH, and H2O were investigated. No silanone trapping product was detected in the reaction of 1 with MesCNO and (Me2SiO)3, while reactions of 1 with MeOH afforded the addition product Mes2Si(OMe)OH (5). The hydrolysis of molybdenum complex 1b afforded silanediol Mes2Si(OH)2 (8) as a main product with a trace amount of Mes2Si(OH)OSiMe3 (9), while that of the tungsten analogue 1a gave siloxysilanol 9 as the sole product, indicating that product distribution in the hydrolysis strikingly depends on the metal fragments. A theoretical investigation revealed that the product distribution difference between tungsten and molybdenum complexes arises from the difference in electrophilicity of the silicon atom in the silanone ligand and that of the lability for oxidative addition of water to the MII–L fragment.

One-electron oxidized salen complexes of Mn(III) and Ni(II) were recently reported to be unique mixed-valence compounds. Their electronic structures are sensitive to the salen ligand and solvation. We systematically investigated a series of one-electron oxidized salen complexes of group 7 metals (Mn(III), Tc(III), and Re(III)) and their group 10 analogues (Ni(II), Pd(II), and Pt(II)) using the general multi-configuration reference quasi-degenerate perturbation theory (GMC-QDPT) which was combined with the three-dimensional reference interaction site model self-consistent field theory (3D-RISM-SCF) to incorporate the solvation effect. The calculated absorption spectra and electronic structures agree with the experimental observation. The one-electron oxidized salen complexes of group 10 metals with a symmetrical salen ligand have a delocalized electronic structure belonging to class III (Robin–Day classification) in weakly polar solvents. The tendency for taking a delocalized electronic structure increases in the order Pd(II) < Ni(II) < Pt(II). When the salen ligand is asymmetrical, the one-electron oxidized complexes have a localized electronic structure belonging to class II. The group 7 analogues of Mn(III) and Tc(III) have a localized electronic structure belonging to class II even in weakly polar solvents and even with a symmetrical salen ligand. However, the one-electron oxidized Re(III) complex has no mixed-valence nature because one-electron oxidation occurs on the Re center. Theoretical study shows that the solvation effect plays a crucial role in determining the mixed-valence character, class II or III, and thereby its incorporation in the calculation is indispensable for correctly describing geometries, electronic structures, and the inter-valence absorption spectra of these complexes. The d orbital energy is one of the most important factors for determining the localization/delocalization electronic structures in these complexes. Detailed discussion of these factors is presented.

Spin multiplicities and coordination structures of dinitrogen-bridged hetero-dinuclear complexes of 3d metals, (μ-N2)[M(1)(AIP)][M(2)(AIP)] (AIPH = (Z)-1-amino-3-imino-prop-1-ene; M(1), M(2) = V(i) to Co(i)), were investigated using the CASPT2 method. (μ-N2)[V(AIP)][Cr(AIP)] has a low spin doublet ((2)B2) ground state with an η(2)-side-on dinitrogen coordination structure but (μ-N2)[Mn(AIP)][Fe(AIP)] has a high spin octet ((8)A2) ground state with an η(1)-end-on coordination structure. These results are similar to those of the homo-dinuclear Cr and Fe analogues, respectively. In (μ-N2)[Cr(AIP)][M(AIP)] (M = Mn(i), Fe(i), or Co(i)) consisting of an early 3d metal (Cr) and a late one (Mn to Co), on the other hand, we found characteristic features in the geometry and the ground state electronic structure which are different from those of homo-dinuclear analogues. The Cr-Mn complex has a high spin decet ((10)B1) ground state with an η(2)-side-on structure. This decet state has the highest spin multiplicity in the dinuclear transition metal complexes, to our knowledge. The A2 state with a doublet spin multiplicity is moderately less stable than the (10)B1 state. The optimized structures and the molecular orbitals indicate that the Cr atom strongly interacts with the N2 moiety in the (10)B1 state but the Mn atom strongly interacts with the N2 moiety in the (2)A2 state. The Cr-Fe complex has a high spin nonet ((9)B1) ground state with an η(2)-side-on structure like the Cr-Mn complex, but only the Cr-Co complex has a medium spin quartet (4)A2 ground state with an η(2)-side-on structure. The different ground electronic state of the Cr-Co complex arises from the presence of 3d orbitals at low energy. Based on these results, it is concluded that the geometry is determined by the Cr center but the electronic structure and the spin multiplicity are determined by the combination of early and late 3d metals in the dinitrogen-bridged hetero-dinuclear chelates of 3d metals.

Experimentally observed NO dimerization on Cu and Ag surfaces is surprising because binding energy of NO dimer is very small in gas phase. MRMP2, MP2 to MP4, CCSD(T), and DFT studies of NO dimerization on Ag

The spin multiplicities and coordination structures of inverse sandwich-type complexes (ISTCs) of ethylene and dinitrogen molecules with 3d transition metal elements (Sc to Ni), (μ-C2H4)[M(AIP)]2 and (μ-N2)[M(AIP)]2 (AIPH = (Z)-1-amino-3-iminoprop-1-ene; M = Sc to Ni) were investigated by the CASPT2 method. In both ethylene and dinitrogen ISTCs of the early 3d transition metals (Sc to Cr), sandwiched ethylene and dinitrogen ligands coordinate with two metal atoms in an η(2)-side-on form and their ground states have an open-shell singlet spin multiplicity. The η(1)-end-on coordination structure of dinitrogen ISTCs is considerably less stable than the η(2)-side-on form in these metals. For the late 3d transition metals (Mn to Ni), ethylene and dinitrogen ISTCs exhibit interesting similarities and differences in spin multiplicity and structure as follows: in ethylene ISTCs of Mn to Ni, the ground state has an open-shell singlet spin multiplicity like those of the ISTCs of early transition metals. However, the ethylene ligand is considerably distorted, in which the ethylene carbon atoms have a tetrahedral-like structure similar to sp(3) carbon and each of them coordinates with one metal in a μ-η(1):η(1) structure. These geometrical features are completely different from those of ISTCs of the early transition metals. In dinitrogen ISTCs of Mn to Ni, on the other hand, the ground state has a high spin multiplicity from nonet (Mn) to triplet (Ni). The η(2)-side-on coordination structure of the dinitrogen ligand is as stable as the η(1)-end-on form in the Mn complex but the η(1)-end-on structure is more stable than the η(2)-side-on form in the Fe to Ni complexes. All these interesting similarities and differences between ethylene and dinitrogen ISTCs and between the early and late transition metal elements arise from the occupation of several important molecular orbitals., Accepted 18 May 2015

The measurement of the electronic spectra of jet-cooled 4-chloro-7-azaindole dimer (4CAI2) revealed that the Cl substitution substantially suppresses the excited-state double-proton transfer (ESDPT). Quantum chemistry calculation at the CIS level suggested that the change in the intermolecular stretching mode, which promotes ESDPT, is important for the suppression of ESDPT.

A catalytic multiple-proton/hydrogen atom relay in the 7-azaindole-methanol cluster (7AI(MeOH)n, n = 1–3) has been investigated in the gas phase by measuring the mass-resolved vibronic spectra and the dispersed fluorescence spectra of 7AI(MeOH)n (n = 1–3). It has been found that the observation of the visible fluorescence due to the multiple-proton/hydrogen atom relay is cluster-size selective; 7AI(MeOH)2 undergoes an efficient triple-proton/hydrogen atom relay on a ππ∗ and/or πσ∗ surface. The triple-proton/hydrogen atom relay in this cluster also exhibits prominent vibrational-mode selectivity. The excitation of an intermolecular stretch mode (σ1) with the in-phase cooperative motion of the whole hydrogen-bond network accelerates the proton/hydrogen atom relay.

One-electron oxidized Mn(III)- and Ni(II)-salen complexes exhibit unique mixed-valence electronic structures and charge transfer (CT) absorption spectra. We theoretically investigated them to elucidate the reason why the Mn(III)-salen complex takes a localized electronic structure (class II mixed valence compound by Robin-Day classification) and the Ni(II)-analogue has a delocalized one (class III) in solution, where solvation effect was taken into consideration either by the three-dimensional reference interaction site model self-consistent field (3D-RISM-SCF) method or by the mean-field (MF) QM/MM-MD simulation. The geometries of these complexes were optimized by the 3D-RISM-SCF-U-DFT/M06. The vertical excitation energy and the oscillator strength of the first excited state were evaluated by the general multiconfiguration reference quasi-degenerate perturbation theory (GMC-QDPT), including the solvation effect based on either 3D-RISM-SCF- or MF-QM/MM-MD-optimized solvent distribution. The computational results well agree with the experimentally observed absorption spectra and the experimentally proposed electronic structures. The one-electron oxidized Mn(III)-salen complex with a symmetrical salen ligand belongs to the class II, as experimentally reported, in which the excitation from the phenolate anion to the phenoxyl radical moiety occurs. In contrast, the one-electron oxidized Ni(II)-salen complex belongs to the class III, in which the excitation occurs from the doubly occupied delocalized π1 orbital of the salen radical to the singly occupied delocalized π2 orbital; the π1 is a bonding combination of the HOMOs of two phenolate moieties and the π2 is an antibonding combination. Solvation effect is indispensable for correctly describing the mixed-valence character, the geometrical distortion, and the intervalence CT absorption spectra of these complexes. The number of d electrons and the d orbital energy level play crucial roles to provide the localization/delocalization character of these complexes.

The S1-S0 fluorescence excitation and dispersed fluorescence spectra of 9-methylanthracene are measured in a supersonic free jet expansion. Several low-frequency bands assigned to the transitions between the internal rotational levels of the methyl group can not be fitted to the calculated energy levels obtained by the one-dimensional rotor model. We have introduced a two-dimensional model incorporating the coupling of the methyl rotation and an out-of-plane bending motion of the anthracene ring. The calculations based on this model reproduce the intensity distributions in the fluorescence excitation and dispersed fluorescence spectra as well as the frequencies of the internal rotational levels in the S0 and S1 state. � 2006 Elsevier B.V. All rights reserved.

The S 1 –S 0 fluorescence excitation and dispersed fluorescence spectra of 2- and 1-methylanthracene are measured in a supersonic free jet expansion. The barrier heights to internal rotation in the S 0 and S 1 states of 2-methylanthracene are determined to be 69 and 335 cm −1 , respectively, by using a one-dimensional free-rotor model. A prominent 0–0 transition has been observed in the fluorescence excitation spectrum of 1-methylanthracene, but no methyl rotational bands have been detected in both the excitation and dispersed fluorescence spectra. The potential energy curves of the methyl rotation are obtained for 2- and 1-methylanthracene with density functional theory (DFT) calculations and time-dependent (TD)-DFT calculations at the B3LYP/6-31 + G(d,p) level. The barrier heights and the phase of the potential energy curve are very different between 2- and 1-methylanthracene and substantially depend on the electronic state. These differences are consistently explained by a π*−σ* hyperconjugation effect introduced by Nakai and Kawai [Chem. Phys. Lett. 307 (1999) 272].

The dispersed fluorescence spectra have been measured for the 7AI–(H 2 O) n ( n = 1–3) clusters in a supersonic free jet expansion by exciting various vibronic bands in the S 1 state. There has been controversy about the occurrence of the excited-state proton transfer in the n = 2,3 clusters. The absence of visible fluorescence from the tautomer forms of 7AI–(H 2 O) n ( n = 1–3) indicates that the full tautomerization due to photoinduced excited-state proton transfer does not occur during the lifetime of the S 1 state of the normal form each cluster.

A membrane charge is one of the most important factors that affects the permeation of ions through the membrane. For amphoteric membranes such as inorganic membranes, the membrane charge depends on the pH and the electrolytes in the bulk solution. In this paper, we theoretically discuss the permeation of ions through the amphoteric membrane using the advanced amphoteric membrane model. In this model, the membrane charge is determined by the dissociation of the amphoteric membrane material as well as the selective adsorption of ions. We assumed that the system was in the steady-state and there was no volume flow. We also assumed that no ions were adsorbed selectively in order to clearly show the effect of the dissociation of membrane material. As a result of the discussion, it was theoretically predicted that the flux through the amphoteric membrane was maximized with the pH. It is, therefore, possible to select the best condition for a large flux by adjusting the pH of the bulk solution.

It has been reported that the membrane charge of amphoteric membranes such as inorganic membranes depends on the pH and the electrolyte in the bulk solution. To explain these phenomena, we have proposed the advanced amphoteric membrane (AAM) model where the effective membrane charge is determined by the dissociation of the amphoteric membrane material as well as by the selective adsorption of ions. We applied the AAM model to the alumina membranes and microporous glass membranes to characterize their membrane charges. It was concluded that the effective membrane charge of these membranes was determined by the dissociation of membrane material besides the selective adsorption of ions. It was also shown that the dependency of the effective membrane charge on the pH and the electrolyte was well explained by the AAM model.

An anhydrous polymorphic form of alpha,alpha-trehalose was prepared from trehalose dihydrate by two different drying methods: (1) heating under vacuum; and (2) heating in hot air. Preparation of this anhydrous form by vacuum heating showed good reproducibility. This form was characterized by X-ray powder diffraction analysis and differential scanning calorimetry. This anhydrous form was converted to an amorphous phase at 127 degrees C and was found to be hygroscopic. At 43% relative humidity at 25 degrees C, this form rapidly reverted to dihydrate, while the amorphous phase remained unchanged. When an amorphous phase coexisted with this form, the rate of water adsorption to the amorphous phase was slower than that to the amorphous phase alone. These properties of this anhydrous form of alpha,alpha-trehalose may explain the effects of trehalose in dehydration tolerance of plants and insects in the desert.

Inverse sandwich-type complexes (ISTCs), (μ-N2)[M(AIP)]2 (AIPH = (Z)-1-amino-3-imino-prop-1-ene; M = Cr and Fe), were investigated with the CASPT2 method. In the ISTC of Cr, the ground state takes a singlet spin multiplicity. However, the singlet to nonet spin states are close in energy to each other. The thermal average of effective magnetic moments (μeff) of these spin multiplicities is close to the experimental value. The η(2)-side-on coordination structure of N2 is calculated to be more stable than the η(1)-end-on coordination one. This is because the d-orbital of Cr forms a strong dπ-π* bonding interaction with the π* orbital of N2 in molecular plane. In the ISTC of Fe, on the other hand, the ground state takes a septet spin multiplicity, which agrees well with the experimentally reported μeff value. The η(1)-end-on structure of N2 is more stable than the η(2)-side-on structure. In the η(1)-end-on structure, two doubly occupied d-orbitals of Fe can form two dπ-π* bonding interactions. The negative spin density is found on the bridging N2 ligand in the Fe complex but is not in the Cr complex. All these interesting differences between ISTCs of Cr and Fe are discussed on the basis of the electronic structure and bonding nature.

In order to characterize the membrane charge of the alumina membrane, we saw about the information on the membrane charge at first. Then, we pointed out that the effective membrane charge of alumina consists of two parts. One part is the membrane charge due to the dissociation of the ionizable groups of membrane, and the other part is the membrane charge affected by the electrolytes in the bulk solution. Then, we proposed the new membrane model that is the combination of the selective ion adsorption model and the amphoteric membrane model. In this model, the effective membrane charge is determined by the dissociation of the ionizable groups of the membrane and the selective adsorption of ions. We theoretically discussed the effect of the electrolyte concentration, the ionic species and the pH on the effective membrane charge. Then, we showed that this new model, the advanced amphoteric membrane model, can qualitatively explain the phenomena related to the membrane charge. We applied the advanced amphoteric membrane model to the membrane potential of alumina membrane and concluded that the effective membrane charge of the alumina membrane was determined by the dissociation of the ionizable groups and the adsorption of anions.

The membrane potential of the composite membrane, TiO 2 /Al 2 O 3 , and the Al 2 O 3 support were measured to characterize the membrane charge of TiO 2 /Al 2 O 3 membrane and to make clear the effect of Al 2 O 3 support. As the results, it is shown that it is impossible to neglect the effect of the support due to its charge. It is also shown that the TiO 2 /Al 2 O 3 membrane will be bipolar between pH 6.2 and 7.4.

An examination of the relationship between the hydrophobic index of saccharide and gel-liquid crystal transition temperatures in L-α-dipalmitoyl phosphatidylcholine (DPPC)/saccharide systems at a water content of 10 wt% and 70wt% was performed using differential scanning calorimetry. Saccharide at 10 wt% water was found to interact with phospholipids hydrophobically via the hydrophobicity-rich side of the pyranose ring. Molar ratios (pyranose ring/DPPC) were determined as 2 for the DPPClrhamnose system with 8.2 wt% water and for the DPPC/trehalose system at 15.8 wt%. Pyranose would thus appear to form a 2:1 complex with lipid that faces the hydrophobicity-rich side of the pyranose ring. Saccharide with 70 wt% water interacted with the phospholipid hydrophilically through hydration of the saccharide.

The effects of sonication, conducted prior to dehydration by heat drying, on the multilamellar vesicles of L-α-dipalmitoyl phosphatidylcholine (DPPC), DPPC/glucose, DPPC/trehalose or DPPC/maltose systems were examined by differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD). The results were compared with those for the corresponding unsonicated and DPPC systems without saccharide. In the DPPC/glucose system, no clear differences between the unsonicated and sonicated systems were found because glucose did not prevent fusion of vesicles by dehydration. DSC showed one sharp peak at the gel-liquid crystal transition temperature (Tc) of 43°C, indicating that glucose was distributed homogeneously between the DPPC bilayers of the vesicles. Subcells formed by hydrocarbon chains of DPPC changed from the hexagonal gel (Lβ) to the hexagonal liquid crystal (Lα) form at Tc with an increase in temperature, essentially as noted for DPPC systems except for differences in Tc. In the DPPC/disaccharide system, the unsonicated and sonicated systems were clearly different. DSC and XRD of the unsonicated system consistently showed transition from a gel to a liquid crystal state over a wide temperature range, while for the sonicated system, there was only a sharp peak on the DSC curve. The thermal behavior of DPPC/disaccharide systems may be explained as follows. Although disaccharide is distributed homogeneously between the bilayers of multilamellar vesicles, interactions with DPPC depend on the surface curvature of the bilayer. Heating of multilamellar vesicles may possibly result in transition from a gel to a liquid crystal phase since multilamellar vesicles consist of many bilayers differing considerably in their surface curvature, in contrast to sonicated unilamellar vesicles which possess a definite curvature.

Formation of an intermolecular complex between a polymer and a surfactant on the surface of a particle, and its effect on the suspension stability are discussed for the systems (1) kaolinite-sodium dodecyl sulfate (SDS)-polyvinylpyrrolidone (PVP), (2) kaolinite-SDS-hydroxypropylcellulose (HPC), (3) hydroxyapatite (HAP)-SDS-PVP, and (4) HAP-SDS-bovine serum albumin (BSA). The complex is formed by electrostatic and hydrophobic interactions, both of which often operate simultaneously. The effect of the surface complex on the suspension is explained in relation to the mean diameter of the secondary particles and the rheological properties of the suspensions. The significance of these studies for physicochemical and biological sciences is briefly discussed.

From the analysis of the membrane potential, the magnitude of the Donnan potential was calculated by using the values of the measured parameters. The Donnan potential is the electric potential at the inner position located just a little off the interface and mainly reflects the electric charge within the membrane. On the other hand, the zeta (ζ) potential is the potential at the slipping plane. The slipping plane is at the outer position just a little off the interface. Therefore, it is possible to obtain more precise information on the distribution of the membrane charge, especially at the interface, by comparing the Donnan potential with the ζ-potential. According to this concept, we compared the Donnan potential with the ζ-potential measured for the nylon 6 membrane at various pH values. As a result, it is pointed out that the nylon 6 membrane dissociates only around the membrane/bulk solution interface but scarcely within the membrane. Within the membrane, the effective membrane charge is determined by selectivety adsorbed ions. This conclusion suggests that the electrochemical properties of membranes are different from those proposed based on the properties of membrane materials in a aqueous solution.

Foams are dispersed systems of gas particles. The stability of the foams, however, is determined by the property of foam membrane. Foams should, therefore, be studied as membrane systems. In this paper, fundamental properties of the foams are discussed on the basis of the surface chemical behavior of the membrane systems. Besides very stable foams covered with solid films or bimolecular films, less stable foams as well as unstable foams are stabilized by the adsorbed monolayer of foaming agent. These foams are the more stable if the more of the foaming agent is adsorbed the more tightly. Antifoams are classified into foam breakers and foam inhibitors. The foam breaker acts upon the foams already formed, by spreading on the surface of the foam membrane. On the other hand, the foam inhibitor acts to prevent foaming by driving out the foaming agent from the surface of the foam membrane as the result of preferential adsorption.

The surface tension of aqueous solution of arachidonic acid (AA) was measured with a Du Nouy tensiometer at pH 7.80 and various temperatures, and the effect of temperature on the surface properties of AA was investigated. The value of critical micelle concentration (cmc) of AA increased and the surface tension at the cmc, γcmc, decreased as the temperature was raised from 30 to 60°C. The Langmuir constant k concerning the strength of adsorption decreased, the saturated adsorption ammount of AA, Γ∞, at the air-water interface decreased, and the area occupied by an AA molecule at the saturated adsorption, A∞, increased as the temperature was raised. The standard free energy for the adsorption, ΔGad, was of negative value, and the absolute value |ΔGad| became larger as the temperature was raised because of the negative value of the standard enthalpy change ΔHad and the positive value of the standard entropy change ΔSad. The standard free energy of micellization, ΔGm, was of negative value, and it was similarly found that |ΔGm|became larger as the temperature was raised because of the negative value of the standard enthalpy change ΔHm and the positive value of the standard entropy change ΔSm.

Trehalose (Tre) is found at particularly high concentration in anhydrobiotic organisms, and is effective in stabilizing the bilayer membranes of phospholipids in freeze-drying. We studied the mixture of L -α-dipalmitoylphosphatidylcholine (DPPC) and trehalose at various water contents by differential scanning calorimetry (DSC) and the small angle X-ray diffraction method. The Tre intercalated between lipid bilayers and formed complexes, and the excess Tre crystallized as its dihydrate by the addition of water. The amount of the dihydrate was estimated from the peak area in DSC. The experimental values of the molar ratio (Tre/DPPC) of the complexes thus determined were 1:2 and 1:1, and the corresponding expansions of the lamellar spacing were observed by small angle X-ray diffraction.

The effect of simultaneous adsorption of two polymers on the mean diameter, d, of secondary particles of amorphous silica (Micon FN) was studied. The d value was decreased by the adsorption of sodium chondroitin-6-sulfate (Na2Chs) or sodium carboxymethylcellulose (NaCMC), although the amount of Na2Chs or NaCMC adsorbed was lower than that of polyvinylpyrrolidone (PVP), a flocculating agent. The amount of adsorbed Na2Chs or NaCMC decreased in the presence of PVP due to competitive adsorption, but that of PVP increased, due to the disintegration of silica aggregates caused by the adsorption of Na2Chs or NaCMC. The zeta potential of Micon FN became less negative on adsorption of PVP, due to the protrusion of the polymer loop, but became more negative by the adsorption of Na2Chs or NaCMC in either the presence or absence or PVP, indicating that electrostatic ???ulsion is important for the dispersion of silica particles. In the case of PVP, non-electrostatic effects such as steric hindrance and interparticle bridging are dominant factors for the dispersion and flocculation.

The permeability of liposome entrapping insulin through the nasal mucosa of rabbit has been studied and compared with the permeability of insulin solution with or without pretreatment by sodium glycocholate (GC). Insulin entrapped in liposome was not detected in the receiver cell using the diffusion cells with the nasal mucosa. On the other hand, permeability of insulin entrapped in liposome increased after the pretreatment of GC. The phospholipids which result from liposomes, were not observed in the receiver. Also, the GC remaining in the nasal mucosa was measured. Considering the mechanism of permeation of insulin entrapped in liposome through the nasal mucosa, the GC remaining in the nasal mucosa may cause the lysis of liposomes.

The dissociation constants of diclofenac in ethanol-water mixtures, in connection with percutaneous absorption, were determined using the titration method. The acid dissociation constant of sodium diclofenac was decreased by the increase in the concentration of ethanol in the aqueous solution. The results were interpreted in terms of solvent polarity. It is suggested that ethanol, which is used as an enhancer for percutaneous absorption, assumes another role, increasing the proportion of the unionized form of the drug and forming ion pairs in low dielectric media. Also the partition coefficients for diclofenac were measured in an n-octanol/water or buffer system over the pH range from 3 to 8. The distribution behavior of diclofenac is dramatically affected in the presence of added cations. Above pH 7, ion pair formation promotes the distribution of the drug into lipophilic environment.

Nasal drug absorption and the effect of absorption promoters have been studied in rabbits. Nasal mucosa excised from rabbits was mounted as a flat sheet in an in vitro chamber. The increase in the membrane permeability coefficient for sodium chloride indicates the change in the porosity by pretreatment with bile salts. The permeabilities for dextran derivatives were enhanced by pretreatment with sodium glycocholate (GC). The permeability coefficient (P) for fluorescein isothiocyanate diethylaminoethyl dextran (FITC DEAE-dextran, DE) was higher than that for FITC-dextran (DT), and P for FITC dextran sulfate (DS) was lower than that for DT with the same molecular weight. Comparing insulin with dextran of the same molecular weight as insulin, the value of P for insulin induced by pretreatment with GC was higher than that for hydrophilic dextran. The partition coefficient seemed to have much more effect on the nasal membrane transport than the molecular weight of the penetrant.

Concentrations of phosphate and calcium ions, liberated from the surface of hydroxyapatite (HAP) during the adsorption of phosphoserine (PSer), were determined at 30°C. HAP showed a marked incongruent dissolution behavior in the presence of PSer. That is, the concentration of phosphate ion in solution increases with the addition of PSer due to the ion-exchange between PSer and phosphate ion on HAP (molar ratio of the former to the latter=3∶2), whereas the concentration of calcium ion decreases with this release of phosphate ion, because the solubility product of HAP restricts the concentrations of both ions in solution (calculated values of — log (Ca2+)10 (PO43−)6 (OH−)2 were 115.8±1.0). The affinity of PSer to HAP was highest at pH 5.8 where the PSer and the HAP surface had the opposite charges. This electrostatic attraction force between PSer and HAP was shielded to some extent by the addition of KCl.

The nasal drug absorption and the effect of absorption promoters have been studied in rabbits. Nasal mucosa excised from rabbits was mounted as a flat sheet in an in vitro chamber. The result indicates that the change in the porosity of the membrane by pretreatment with bile salts increased the permeability coefficient of sodium chloride in the nasal membrane. The permeabilities of dextran derivatives were enhanced by pretreatment with sodium glycocholate (GC). The permeability coefficient (P) of fluorescein isothiocyanate diethylaminoethyl dextran

Charged membranes have been characterized by many investigators. Their attention has mostly focussed on the fixed charge of uniform membranes, but in recent years it has been pointed out that real membranes are not perfectly homogeneous. In this paper, the effect of selective ion adsorption on the membrane potential has been investigated theoretically in order to find a suitable model for a real membrane. The membrane considered here is, for simplicity, one which has a positive fixed charge and adsorbs anions selectively. As a result, it is found that the membrane potential shows a minimum with the decrease of bulk concentration. This phenomenon, which results from changes in the effective membrane charge density, is due to the variation of the amount of ions adsorbed by the membrane. The theory is applied to the analysis of the membrane potential of a collodion membrane, and it is shown that the theory is in good agreement with experimental data. Our model is adequate for obtaining information on the fixed membrane charge density, the saturated amount of adsorbed ion and the adsorption coefficient by the analysis of the membrane potential. The positive deviation of the products of the partition coefficients of co-ion and counter-ion for the membrane charge is well explained by the model.

The solvent-dependent visible spectral shifts of a cationic dye, methylene blue (MB), are correlated with Taft's generalized polarity and generalized proton donor scales, π and α, respectively. The solvent effects on the ET(30) value of a zwitterionic probe, 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridino)-phenoxide (DTPP) have also been presented as a function of π and α (M. J. Kamlet, J. L. M. Abboud, and R. W. Taft, Prog. Phys. Org. Chem. 13, 485 (1981)). The wavelengths of adsorption maxima of MB for micellar and liposomal surfaces are combined with the reported ET(30) values of DTPP for the surfaces (K. A. Zachariasse, N. Van Phuc, and B. Kozankiewicz, J. Phys. Chem. 85, 2676 (1981)) and solved with respect to π and α. It is found that, in the head group layer of micelles and liposomes, the magnitude of dipole interactions is a little smaller than that in the bulk water phase, but the proton donor-acceptor interactions are largely reduced. The somewhat higher values of π and α observed for the sodium tetradecyl sulfate micelle are attributed to the enhanced dipole and proton donor ability of hydrated waters around the sodium ion in the head group layer. The weakest proton donor ability in liposomes is interpreted in terms of the structural properties of the surface layer. It is also found that a pair of π (1.0) and α (0.6) for a micellar surface made it possible to calculate the “effective dielectric constants,” 76, 47, and 32, for MB, DTPP, and prydinium iodide derivatives, respectively. These values are consistent with the experimental values of the effective dielectric constants.

The degradation of Methyl Orange (MO) by singlet oxygen was inhibited by the addition of α-, β-, and γ-cyclodextrins (CD’s) to an aqueous solution. The protective effect of the CD’s against the MO oxidation decreased in this order; α->γ-\gtrsimβ-CD. From the relation between the rate constant of MO oxidation and the free MO concentration, evaluated by using the formation constants of CD’s with MO, it was found that the MO included by α and γ-CD’s is not decomposed by singlet oxygen, whereas the MO included by β-CD is oxidized by singlet oxygen. The inner cavity of α- or γ-CD well fit for the inclusion of one or two MO molecules respectively, and the access of singlet oxygen to the azo group of the included MO molecule is sterically inhibited. The finding that β-CD has smaller enthalpy and larger entropy changes relevant to the formation of the MO–CD complex than those of α- and γ-CD’s suggested the less tight inclusion of one MO molecule in the cavity of β-CD. Such a loose inclusion of MO by β-CD resulted...

Photoelectron transfer from ethylene diamine tetraacetate to Methyl viologen (MV2+) is studied with 3,3′-dialkyl thiacarbocyanines as sensitizers. Reaction efficiency is remarkably enhanced when the sensitizer dye is solubilized in the micellar phase of heptaethylene glycol monododecyl ether. Experimentally, it is found that tbe dyes locate in the less polar and more viscous micellar environment than in aqueous phase. The enhancement of reaction efficiency is interpreted by the stabilization of excited state of the dyes in the micellar microenvironments.

The lyotropic and thermotropic olymorphisms of synthetic phosphatidylcholine (DMPC, DPPC, DSPC) and phosphatidylethanolamine (DPPE) are investigated by means of differential scanning calorimetry. The thermal phase transitions of the anhydrated phase and the hydrated lamellar phase of PCs are reversible, while the transition of anhydrated DPPE is irreversible. The spreading pressures of the anhydrated and hydrated lamellar phases are measured on water. The spreading pressure from the lamellar phase of DMPC shows a steep increment at the gel-liquid crystal transition temperature. The anhydrated phase of the phospholipid has a higher spreading pressure than that from the hydrated lamellar phase.

There is a flat region (plateau region) ascribed to the transition from monolayer to bilayer in the surface pressure ( F )-area ( A ) isotherm of poly-γ-methyl- l -glutamate (PMLG) at the air/water interface. The change in entropy from initial to final state of this transition is very small and negative. This indicates that the order in the monolayer and bilayer states is almost the same but that the former is a little more random. At or below 20°C, the monolayer of palmitic acid (PA) forms a solid condensed film and no difference in the F - A isotherm was detected regardless of temperature. However, there is a break at about 16.8°C in the curve of temperature versus surface pressure of the flat region in the F - A isotherm corresponding to the collapse of the PA monolayer. This suggests that the monolayer states of PA above and below 16.8°C are different. PA at or above 20°C is more miscible with PMLG in the monolayer state than PA at or below 15°C. The difference between miscibility of PMLG in the monolayer state and PA at or above 20°C and at or below 15°C can perhaps be ascribed to the difference between the monolayer states of PA above and below ca. 16.8°C.

The objectives of this study were to evaluate the size of the diclofenac ion and the electrical behavior of diclofenac salts (DM; M = Li, Na, or K) in ethanol/water mixtures. The molar conductance of DM in aqueous solution was measured in a dilute concentration range of < 10 mol.m-3 at 25 degrees C. The Fuoss-Onsager conductance equation for unassociated electrolytes was used to determine the limiting molar conductance (lambda degrees) of DM. The molar conductivity of DM at a finite concentration was, however, larger than the value calculated by the Fuoss-Onsager limiting law. To correct the difference in the experimental data, two equations were employed to fit the experimental molar conductance of DM. The size of the diclofenac ion was calculated from the limiting molar conductance and compared with the values obtained by the Fedors method and the apparent ionization constant (pKa) of sodium diclofenac in ethanol/water mixture. The Walden products of DM increased up to 20% (w/w) ethanol, but above this concentration of ethanol they decreased. Specific interactions between the ions and solvent are discussed.

Phospholipid spreads as monolayer at air/water and oil/water interfaces. Interfacial pressure of the monolayer in equilibrium with a definite bulk phase of the lipid, (equilibrium) spreading pressure, depends on lyotropic and thermotropic polymorphic state of the lipid bulk phase. Phosphatidylcholine (PC) in hydrated liquid crystalline state (bilayers in L alpha state) gives an appreciably large value of spreading pressure, 45-46 mN/m. Monolayer-bilayer equilibrium of a neutral lipid-phospholipid mixture is determined by miscibilities of the lipids in mixed monolayer, PC bilayer and bulk (liquid or solid) phase of the neutral lipid. A neutral lipid of limited solubility in PC bilayer forms a separate phase in aqueous medium. The phase is stabilized as small particles in the medium by PC monolayer at the particle surface. The monolayer is in equilibrium with the bilayer. This sort of equilibrium plays important roles in formation and catabolism of triglyceride- and cholesteryl ester-rich lipoprotein particles in animal plasma. The equilibrium is a critical factor also in stabilization of aqueous dispersion of lipophilic vitamin (neutral lipid). Coexistence of emulsion particles (neutral lipid core covered with PC monolayer) and vesicles made of PC bilayer are observed in a stable dispersion.

12-Hydroxystearic acid was stacked to give a lamellar structure. 12-Hydroxy groups formed hydrogen bond sequences along the a-axis. The hydrocarbon chains took approximately an all-trans conformation, but might be slightly bent because of the 12-hydroxy group.